The present invention relates to a supercharging pressure control with a turbocharger of an internal combustion engine, and in particular, it relates to a supercharging pressure control with a turbocharger having an electric motor for adjusting the supercharging pressure.
The turbocharger is a device for enhancing performance of the engine by compressing the intake air with the use of exhaust gas of the engine. A basic structure of the turbocharger includes a turbine and a compressor provided to opposing ends of a rotary shaft. The compressor is positioned on the air intake side and the turbine is positioned on the exhaust side. The turbine is rotated by the exhaust gas flow to drive the compressor. The intake air is compressed by the rotating compressor. The turbocharger provides a high efficiency by using the energy of exhaust gas, which otherwise is useless. For this reason, the turbocharger has been conventionally used. However, there have been some problems with regard to the turbocharger. For example, when the engine speed is low, the efficiency is low because the exhaust gas flow is low. When the engine rotational speed rises high enough to produce high efficiency, there is a time delay before high efficiency is produced.
One approach for supplementing shortage of output power of the supercharger is discussed in the Japanese Patent Publication No. 8-182382. A turbocharger is described having an electric motor incorporated into the turbocharger to drive a turbine forcibly so as to produce a target supercharging pressure. Electricity supply to the motor is controlled in accordance with the difference between an actual supercharging pressure and a target supercharging pressure obtained by searching a table based on operating conditions.
Japanese Patent Application Publication No. 2003-239755 discloses a supercharging pressure control apparatus in which a supercharging pressure control is additionally provided by another controller than a control by using an electric motor. In this apparatus, control is performed to reduce consumption of electricity. According to this technique, an output characteristic and/or a fuel cost can be also improved because the supercharging pressure can be controlled without interference among multiple controls for the electric motor and other control components.
However, the apparatus of the Japanese Patent Application Publication No. 8-182382 takes into consideration only the electric motor as means for controlling the supercharging pressure. Therefore, when multiple controllers are provided, various supercharging pressure controls by individual controller may interfere with each other.
The apparatus disclosed in the Japanese Patent Application Publication No. 2003-239755 is not necessarily directed to a scheme which does not use an electric motor. According to the disclosed control technique, the electric motor is always used while the actual supercharging pressure is smaller than a target supercharging pressure. Therefore, consumption of electricity would be high. Even if a predetermined threshold value for suspending the use of the electric motor is established, adjustment in a trial-and-error manner is required in advance. Moreover, since many setup maps including, for example, a map doe supercharging pressure adjustment values for the electric motor (that is, a target value map) are additionally required, increasing man-hours for set-up.
Thus, there is a need for an engine with a supercharger wherein multiple supercharging pressure control devices can be adjusted using a relatively small number of parameters while avoiding interferences among the multiple control devices.